Circuit Description
The body control module (BCM) uses the ambient light sensor signal to control the Daytime Running Lamps (DRL) System. The ambient light sensor is connected directly to the BCM.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2648 Ambient Light Low Reference Circuit
Conditions for Running the DTC
| • | Voltage supplied to the module is in the normal operating voltage range, approximately 10-16 volts. |
| • | The DRL feature must be enabled. |
Conditions for Setting the DTC
| • | The BCM detects a short to battery positive voltage or an open the DRL ambient light sensor low reference circuit. |
| • | The BCM detects a open in the ambient light sensor signal circuit. |
| • | The condition must be present for more than 1 second. |
Action Taken When the DTC Sets
| • | The BCM stores DTC B2648 in memory. |
| • | The SERVICE VEHICLE SOON telltale illuminates. |
| • | The headlamps, the park lamps, the tail lamps and the marker lamps illuminate to low light intensity. |
Conditions for Clearing the DTC
| • | A current DTC B2648 clears when the BCM no longer detects the fault in the signal circuit or the low reference circuit of the DRL ambient light sensor. |
| • | A history DTC B2648 clears after 100 consecutive ignition cycles. |
| • | The BCM receives the Clear Code command from the scan tool. |
Diagnostic Aids
| • | If the DTC B2648 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections . |
| • | An intermittent short to voltage or an open in the following locations may cause an intermittent malfunction to occur: |
| - | The low reference circuit of the DRL ambient light sensor |
| - | The sensor circuit of the DRL ambient light sensor. |
| - | The ambient light sensor |
| - | The BCM |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference: Master Electrical Component List | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the Ambient Light Sensor parameter is within the specified range? | 1.5-6 V | Go to Diagnostic Aids | Go to Step 3 |
3 |
Does the scan tool indicate that the Ambient Light Sensor parameter is greater than the specified value? | 6 V | Go to Step 4 | Go to Step 5 |
4 |
Does the scan tool indicate that the Ambient Light Sensor parameter is less than the specified value? | 1.5 V | Go to Step 8 | Go to Step 6 |
5 | Test the signal circuit of the ambient light sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
6 | Test the signal circuit of the ambient light sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 7 |
7 | Test the low reference circuit of the ambient light sensor for a high resistance, a short to voltage, or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
8 | Inspect for a high resistance at the harness connector of the ambient light sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 |
9 | Inspect for a high resistance at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
10 | Replace the ambient light sensor. Refer to Daytime Running Lamp (DRL) Ambient Light Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
